Instrument Performance Evaluation, comparing ISO and NORSOK I-106 Dr Paul Holland, EffecTech Group & Jon Carlsen, Norsk Analyse North Sea Flow

Transcription

1 Instrument Performance Evaluation, comparing ISO and NORSOK I-106 Dr Paul Holland, EffecTech Group & Jon Carlsen, Norsk Analyse North Sea Flow Measurement Workshop 2017

2 Overview of presentation Importance of the GC and its performance Importance of a good quality calibration gas Introduce Norsok I-106 test & ISO and highlight different evaluation approaches Highlight some of the additional benefits from the ISO approach Results of using an ISO to generate a Norsok test report Summary 2

3 Fit for purpose? Sometimes it s obvious if equipment is fit for purpose.. 3

4 Fit for purpose? Sometimes it is not obvious.. 4

5 Gas Quality instrumentation (which to choose?) Answer.Best performing instrument

6 Natural Gas Quality Measurement Composition (content) of natural gas Inert gases Nitrogen, carbon dioxide, helium, argon Hydrocarbons Methane, ethane, propane, iso-butane, n-butane, pentanes, hexanes +... Properties (characteristics) of natural gas Calorific value, Wobbe number, standard density (ISO 6976) Compression factor, line density (ISO 12213, AGA 8) Hydrocarbon dew point (ISO 23874) Emission factors (BS 8609) 6

7 Financial risks in energy metering Annual Value / 4,500,000 4,000,000 3,500,000 3,000,000 2,500,000 2,000,000 Typical gas fired power station Power output : 500 MW Energy Price : 60 / MWh 1,500,000 1,000, ,000 0 Typical U(Energy) / %

8 NORSOK I-106 BS EN ISO 10723

9 Norsok I-106 ISO Published 2014 Norwegian Standard Defines pass / fail criteria of 0.3% for GCV based on: Linearity Repeatability Uncertainty Published 2012 International Standard Defines a method, OIML & GUM compliant No pass / fail criteria Establishes Bias Uncertainty Bias and uncertainty compared to established limits

10 Calibration gas The gas chromatograph is a comparator wrist watch analogy calibration gas principal driver for accuracy of measurements inaccuracies in the calibration gas will produce errors in stream gas results NORSOK specifies uncertainty limits for calibration and test gases (Table2) ISO does not specify but requires uncertainties which are used in the calculations

11 Issues: Low temperature

12 Using a non-homogeneous calibration gas Cup of tea analogy

13 Repeatability Comparison Norsok ISO Component range (mole %) 0 to to 100 SD (mole %) U RXi/ Component Range (mol%) Not set SD (mole %) U (mol %) mol % NORSOK ISO 6974

14 Why does ISO not set a repeatability criteria? Now common practice to accept errors in the measurement of component amount fractions provided their effect does not give rise to unacceptable errors in physical properties. Question: If the repeatability of 50 ppm nitrogen in natural gas was greater than the defined limit, what would the effect be on the calculated calorific value? Answer:.A very small effect.should this instrument fail? The ISO provides data which can be compared to Maximum Permissible Bias (MPB) & Maximum Permissible Error (MPE) limits.

15 Linearity Comparison Norsok 3 point check Area amount fraction %mol/mol ISO point check Area amount fraction %mol/mol Can only describe a linear response Can describe a response up to 3 rd order polynomial

16 Dealing with non-linearity NORSOK Determines the maximum difference between the measured and reference values ISO GLS regression analysis to determine best fit polynomial

17 ISO linearity results

18 Non-linear response errors 120 instrument response assumed response true response amount fraction / (%mol/mol)

19 Combining uncertainties - NORSOK 19

20 Modelling performance using ISO The ISO models the GC performance Linearity Repeatability Calibration gas composition & uncertainty Monte Carlo is run on 10,000 simulated gas compositions to establish Mean error Bias Uncertainty on the error

21 Errors and uncertainties on errors E(CV SUP ) / MJ.m methane content / (% mol/mol)

22 Error Distribution E(CV SUP ) / MJ.m methane content / (% mol/mol)

23 Mean Error (Bias) E(CV SUP ) / MJ.m methane content / (%mol/mol) mean error = bias - B(P) δp MPB Maximum Permissible Bias (MPB)

24 Uncertainty on Mean Error E(CV SUP ) / MJ.m methane content / (%mol/mol) uncertainty on the mean error uncertainty on bias - U(B(P)) Maximum Permissible Error (MPE) ( P ) MPE δp + U δ c

25 Errors and Uncertainties - Summary

26 Uncertainty Comparison Norsok ISO (UK specification) Property Uncertainty Gross CV < 0.3% Property Gross CV Gross CV Uncertainty MPB < 0.09 MJ.m 3 MPE < 0.18 MJ.m 3 MJ.m 3 (0.45%)

27 Additional advantages of ISO

28 Optimising Calibration Gas Design x C1,cal = 0.88 mean E(CV) = ± MJ.m -3 x C1,cal = 0.81 mean E(CV) = ± MJ.m -3

29 Operating the GC in a type 1 mode (ISO6974)

30 Type 1 mode vs Type 2 mode

31 Calibration gas reduce dewpoint = increase fill pressure response / (peak area) y=f ass (x) y=f true (x) x cal content / (% mol/mol)

32 Simulating a NORSOK Test using ISO data 32

33 Simulating a NORSOK Test using ISO data Danalyser Simulated Real Component Linearity Uncertainty Linearity Uncertainty Uncertainty Uncertainty K =2 K =2 U LXi C C C ic nc neoc ic nc C N CO O U HS (%rel) 0.18% 0.20% Ums (% rel) 0.18% 0.20% U EF (%rel) 0.22% 0.24% U LXi 33

34 Simulating a NORSOK Test using ISO data Encal Simulated Real Component Linearity Uncertainty Linearity Uncertainty Uncertainty Uncertainty K =2 K =2 U LXi C C C ic nc neoc ic nc C N CO O U HS (%rel) 0.03% 0.04% Ums (% rel) 0.04% 0.06% U EF (%rel) 0.04% 0.06% U LXi 34

35 Simulating a NORSOK Test using ISO data Maxum II Simulated Real Component Linearity Uncertainty Linearity Uncertainty Uncertainty Uncertainty K =2 K =2 U LXi C C C ic nc neoc ic nc C N CO O U HS (%rel) 0.04% 0.05% Ums (% rel) 0.04% 0.05% U EF (%rel) 0.05% 0.06% U LXi 35

36 Summary Norsok test & ISO both determine instrument performance ISO has some additional advantages: Accurately model instrument response characteristics (up to 3 rd order polynomial) Determine uncertainties over range or determine the instrument range within a given uncertainty Provides data for GC to be operated in Type 1 mode according to ISO 6974 (minimising errors) Determine optimum calibration gas composition Decide if a new stream can be added to an existing GC Identify which component is at fault if issues are identified with GC Determine Limits of Detection (LOD) ISO calibration certificate can be issued for Emissions Trading Requirements (EU/ETS) Can be used to simulate NORSOK test results

37 Contact details Dr Paul Holland tel : +44 (0) fax : +44 (0) paul.holland@effectech.co.uk web-site :